Transmission system



` I l 2 May 17 1927' R. v. l.. HARTLEY 6 9100 TRANsMIssoN SYSTEM Filed Dec, 21. 192s Patented May 17,' 1927.

UMTED STATES PATE-NT OFFICE.

nEtAIlLPHI V. L. H ARTLE'Y, 0F SOUTH ORANGE, NEW JERSEY, ASSIGNOB T0 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N; Y., A CORPORATION OF NEW YORK.

TRANSMISSION SYSTEM'.

Application filed December 2'1, 1923. Serial No. 681,926.

This invention relates to transmission systems, and more particularly, it relates to means for translating electric energy into mechanical energy or into energy of a different form and has for an object to increase the transmission efiiciency of the translation.

As is well known in the art an electric line of a plurality of-sections, each. section comprisinga series inductance and a shunt lo capacity may be made to give a substantially constant transmission over a wide range of .frequencies such as the range of importance in speech or music. In order that the lcurrents transmitted along such a line may be transferred into acoustic waves, it is proposed in accordance with one form of this Ainvention to employ each of the series inoluctances of an relectric line as the energizing winding for operating a vibrating member strictly in accordance with the electrical vibration. Each vibrating member may, for example, comprise a diaphragm forming a side wall for an air chamber of appreciable area. These air chambers are connected to short small diameter tubes so that said air chambers and said tubes may be adjusted to y f give an acoustic filter in which the masses of the air in the tubes and the elasticities of the air in thechambers cooperate to determine the transmission characteristics. If desired one end of the acoustic filter may be connected to the small end of a loud speaking horn so that the vibration of the air' in the air chamber is vproduced by the concerted action of the) diaphragms and will be suitably coupled and radiated to the outsid air in the form of sound waves.

Referring to the drawing Fig. lrepresents an electric filter and an acoustic filter 'com-- bined in accordance with the present invention and' Fig. 2 is a cross sectional View of the acoustic filter of Fig. 1 taken in the plane marked 2, 2.

The electric wave filter illustrated in Fig. 1 comprises a plurality of series inducf tances 3, 4 and 5 coupled by shunt capacities 6, 7, 8 and 9 so as to form anielectric wave filter of a plurality of sections, each section comprising a series induct'ance and a shunt capacity. Such a filter is ofthe wellquency range below a cut-off frequency while U. S. patent to Campbell No. 1,227,119 of Ma 22, 1917, on electric wavefilters.

ach of the inductances 3, 4 and 5 is divided into two sections and mounted' on the ends of the magnet members 10, 11 and 12. In close proximity to the ends of these magnets are mounted thev metallic diaphragms 13, 14 and 15, respectively. These diaphgrams 13 to 15 constitute-portions of the side walls enclosing the air chambers 16, 17 and 18 of an acoustic filter. Air chamber 16' is coupled to the adjacent'air chamber 19 -and to the outer air by the short tube 20 of small diameter which leads through the side wall of air chamber 16 to air chamber 1 9, air chamber 19 being coupled to the outer air by an apertured member 21 which will be described later. and 17 are connected by the short tube 22. Air chambers 17 and 18 are connected by the short tube. 23 and air chamber 18 is connected to the small enu of a loud speaking horn 24 by a tube 25. The tubes 20, 22,

23 and 25. are suitably mounted to project through the side wall separating adjacent chambers. The side walls connecting adjacent chambers are preferablyrigid so that the sole means for causing sound waves in one chamber to produce sound waves in an A ir chambers 16'. y

adjacent air chamber is by means of the coupling tube.

The acoustic line just described is of a plurality of sections 4and comprises airv acoustic line depends upon the inertance or -mass per unit area of the fluid of the line-\ and the capacitance or stiffness per unit area chambers connected to each other or to the of Ithe fluid. Since the impedance of fluidf'in a relatively short small diameter tribe` is proportional to the rate of change of the applied force and has the effect of inertia, it..

may beconsidered as an i: ertance. the

other hand, the, application ,ofl force'lto a fluid contained, in a chamber, results in a A compression and expansion of the fluids so that the impedance of such a member is 'in the nature of a capacitance. The arrangement ofthe capacities and the inertances Ais similar to that of the inductances and capacities of an electric Wave filter of a plurality of sections, each section comprising a series inductance and a shunt capacity so that the acoustic filter may be desi ed toA pass with negligible attenuation a wi e range of frequencies of sound Waves, while substantially suppressing frequencies outside said range.

The analogy existing between the .propcrt-ies of an acoustic filter having inertanzes and cap-acitances and those of an electric wave filter havingmductances andcapaclties is set forth in some detail byl G. W.

Stewart in the March 1921 issue of the Physical Review at page 321 and vin the December 1922 issue of the Physical Reviewat page 528. It is shown in these articles that the impedance of an acoustic filter to the follows:

1 2 i Lomfmi' L i where L is the series 'inductance, C the shunt i* `ca acity, and Ik the cut-off frequency. 40

eferring back now to the acoustic filter disclosed in Fig. 1, if the volume of each chamber 16 to 18`is represented byV and the density of the fluid contained therein by p and if a represents-the velocity of lsound inair and le, the direct measure of ease of Vflow througheach of the tubes 420,522,223 and 25, then the quantity kl designates the `mass or inertia of the vibratory-air in thewshorti tube in Fig. leper unit current 'and the quan-- tity' is proportional to the capacity of the resonator. lBy analogyto the. formula of an electric wave filter itfollows that the following formulae' determine the range of frequenciesof sound waves transmitted ,by the acoustic filter disclosedin E ig. 1',

The acoustic filter is preferably 4terminated vat either end with a half'section tei'- minationi, This lmay be dorre by vmaking each of thekchamber'sl19 and 38 of one half the volume of a chamber lfor a `fullsection.

As described above the end chamber 19 is closed by a perforated plate 21. The openings inthis plate should be uniformly distributed and should be of such a number and "size that the impedance presented to the air 7` passing-through the openings is substantially equal to the surge impedance of the acoustic filter. The Limpedance of the 'horn' 24 should, also be equal to the surge impedance of the 'acoustic filter. y

The electric filter of Fig. 1 by an output transformer 30 is coupled to the output of a suitable amplifier 31 which, in turn, is connected by an input transformer 32 to a telephone trans1nitter33. The electric wave filter is, therefore, connected to receive amplified speech or music frequencies from the transmitter 33, and the alternating current windings 3, 4 and 5 will produce the vibration-of the diaphragms 13,V 14 and 15 in accordance with the electrical vibrations and the vibratory energy set up thereby in the air chambers 16, 17 and 18 will be accumula-- tively impressed upon the small end of horn 24 and radiated to the outside air as sound waves corresponding to the character of the electric currents impressed upon the alternating current ywindings 3, 4 and 5 by triansmitter 33. f t i The velocity of electrical Wave transmission through the electric filter should pref- 'erably be made the same as the velocity of transmission of the sound waves through the acoustic channel by suitably adjusting the values of the inductance and capacity of the e electric lter and the inertance and` capacitance o f the acoustic filter. Ifthese `values,

`are adjusted according to the above formulae,

togive the saine cut-ofi' frequency for both the acoustic and electrical filters, it will be found that the velocity of transmission in the two .filters will be the same. The same velocity of transmission in thetwo filters insures that the waves arriving' at the end of the acoustic `filter from each of the dia- -110- phragms will be in phase and will .therefore give an additive effect.

.In order to reduce reflection losses it generally `Will be preferable .to terminate the e'nd of the electric filter opposite-the trans- 115 mitter 3.7- with an impedance or resistance 35 ,of an impedance equalto the surge impedance of the filter as' seen from -its terminals; and it will also .be preferable to have the impedance looking-'from the electric '120.

filter towards the amplifier 31 equal to the surge impedance of the electric filter. If'lhe particular arrangement disclosed for prdcing an. ,operative44 relationship between thealternating current 'windings 3, 4 and 5, L25

lthe` diaphragms' and the magnets is shown 'for illustrative purposes` only, si-I'ce vvarious types of electromagnetic structures known in). i 'i -the art may be employed'. forL causing the efficient vibration of the armatures or dia- -130 5-made without departing in anywise from-- phragms 13 to 15 in accordance with the electric" currents inthe energizing windings. It is also to be understood that various lother modifications of this invention may be the spirit of this invention as defined in the appended claims.

'lhe invention claimed is: i

1. In combination, an acoustic filter of a plurality of sections, each section comprising an enclosed air chamber, an electric filter comprising a line of a plurality of sections, each section comprising an impedance in shunt with the line and an impedance iii series with the line,"one of said impedances in each of said sections comprising an inductance, and means for causingthe electrical currents flowing through each of said inductances to produce vibratory energy in one of said air chambers.

2. In combination, an acoustic filter'of a plurality of sections, each section comprising an inertance and a capacitance, said capacitance in each section comprising an air chamber, an electric filter comprising a line of a plurality of sections, each section comprising a shunt impedance and a series inductance, and means for coupling each of said inductances to a capacitance of said acoustic filter to cause the alternating currents present in each of said inductances to produce corresponding sound waves in one of said air chambers.

3. In combination, an acoustic filter designed to pass a .wide band of wave frequencies with negligible attenuation comprising an air chamber, a short tubular memberl leading from said air chamber, a loud speaking horn coupled to said filter and arranged to transmit to the open air sound Waves passing through saidtubular member, an electric filter designed to'transmit substantially the same band of -wave frequencies as said acoustic filter comprising an inductance, and means for causing alternating currents "from said inductance to produce sound wavesv in said air chamber.

4. In combination, anacoustic filter comprising a series of inertances, a capacitance in shunt to each of said inertances, each of said capacitances comprising an air chamber, an electric line comprising a plurality of inductances, means for causing alternating currents in each of. said inductances to produce sound waves in one of saidy air chambers, andmeans for insuring that the waves produced in each of. said air chambers on Iarriving at one end of said acoustic filter acta'ccumulative'ly. Y

5. In combination, an acoustic filter comprising a series of relativelynarrow tubu'- lar members, chambers of relativelylarge area connectingsucceeding tubular members, an electric line of a pluralitysof sections, each section comprising a shunt capacity and a series inductance, and means for causing alternating currents in each of said inductances to produce corresponding sound waves in one of said air chambers.

6. In combination, an acousticfilter comprising a series of air chambers, a relatively narrow tubular member for connecting adjacent cliamhei's, each of a plurality of said chambers comprising an enclosed wall having a flexible portion, an electric line of a plurality of sections, each sec/tion comprising a shunt impedance and a series impedance, one of said impedaiices of' each, seo tion comprising an inductance, and means for causing alternating currentsfpresent in each of said inductances to produce the mechanical vibration of the flexible portion of one of said side walls.

7 In combination, an acoustic filter comprising a series of 'relatively-narrow tubular members,- air chambers of' relatively large area connecting succeeding tubular members, a diaphragm forming a portionof one side Wall of each of said chambers, an electric line of a plurality of sections, each section comprising 4a 7 shunt capacity and a series inductance, and means for causing alternating currents in each of said inductances to produce the mechanical vibration of one of said diaphragm's. f

8. In combination, an acoustic filter comprising a series of relatively narrow tubular members, chambers of relatively large area connecting succeeding tubular members, said chambers and n`said tubular members being arranged to provide a filter of negligible atftenuation for a wide range of frequencies of importance in speech, an electric filter comprising a line of a' plurality of sections, ea'ch section comprising a series inductance and a shunt capacity, said inductances andl capacities having values adjusted to cause said filter to transmit with negligible attenuation electric cur-rents of awide range of frequencies of importance in speech, and means for causing alternating currents present in each of said inductances to produce sound waves in each of' said chambers..

9. In combination, an acoustic filter comprising a series of relatively narrow tubular members andl chambers of relatively large area connecting succeeding tubular members, said tubular members and chambers being arranged and adjusted to produce an acoustic filter having a substantially l constant transmission characteristic for a wide rang'e'of. frequencies of importance in speech, a diaphragm forming a portion of the enclosure of each of said chambers, an electric filter comprising a line of a vpluralityof sections, each section comprising ay v series inductance anda shunt capacity, said inductancesI and capacities having such Values that said electric filter transmits with' la substantially constant transmission chariso acteristic alternating currents of a wide range of frequencies of importance in speech, and rans for causing-alternatingy currents presentin each of saidinductance's to produce the mechanical vibration of one of said diaphragms.

l0. In combination, an electric filter of a plurality .of sections, each section compris- ,ing a serles inductance andI a shunt capacity, an acoustic -filter of a plurality of sec- ,t1ons, each section comprlsmg a serles of relatively narrow tubular members, an air one. of said chambers, and means for ter-l minating each endl of eachofsaid filters in an impedance substantially surge impedance of the lter.

In witness whereof, I hereunto subscribe RALPHIV. L. HARTLEY.

equal to the v my name this 14th day of December A. D., y 1923. 

